A 500 MeV Low Operating Cost Electron Linac

A 500 MeV linac has been constructed and operated since Dec. 1980 at ETL in Tsukuba for the generation of high intensity photons and pions and for the electron injection to a 600 MeV storage ring and a 150 MeV beam stretcher. The linac consists of an injector with a triode type electron gun and an inflector and three kinds of twenty linearly tapered iris type accelerating sections, of which four sections are 2.3 m long and sixteen sections 3 m long. Rf power at a frequency of 2856 MHz is provided by seven 25 MW klystrons with an improved efficiency of about 50 % to save the power consumption to about 70 % of that of the ordinary linac. The maximum beam duty cycle is 0.24 %. To avoid the cumulative beam blow-up, special attention has been paid to the design of the linearly tapered iris type accelerating section and the configuration of twenty sections and eleven quadrupole doublets and a triplet. For the economical beam sharing, the beams with three different energies from low, medium and high energy sections are simultaneously provided to four experimental arears by means of the combination of three pulsed coils and four beam transport systems.